1. Field of the Invention
The present invention relates generally to the field of apparatus for the handling of continuous webs of paper and, more particularly, to apparatus for handling a continuous web of Z-fold (fan-fold), tractor-feed computer paper that is discharged from a printer, such as a printer associated with a computer.
2. Background Discussion
It is well known that many computer printers, especially high speed printers associated with large computers, print on a continuous web of Z-fold (also often referred to as "fan-fold" or "accordion-fold") computer paper that has a row of sprocket or pin drive holes along each side edge. In operation, motorized drive sprockets or pin-studded belts associated with the printers engage these drive holes, thereby enabling the continuous webs of computer paper to be advanced at a selected printing speed through the printers. Such belt-type paper drives are sometimes referred to as "tractor" drives because of the resemblance of the studded paper drive belts to tractor treads.
Such continuous Z-fold paper is "divided" into "sheets," for example, 11 by 14 inches or 81/2 by 11 inches in size, that are separable one from another along transverse fold lines, the paper being slightly perforated or otherwise weakened at these fold lines so that, as desired or needed, the sheets can be easily separated one from another by tearing or "bursting."
Ordinarily, the two narrow strips along the sides of the paper through which the two opposing lines of drive holes are formed are also scored so they can be easily separated from the rest of the sheets. In this manner, individual computer printout sheets, comparable to standard sheets of paper, can easily be obtained for filing, copying or the like.
During printing, however, it is ordinarily highly desirable, if not necessary, for the sheets of the continuous web of computer paper to remain joined to one another so that the proper printing continuity is automatically maintained without the need for operator intervention or supervision. Although there are some single sheet printers which print on individual sheets of paper, such printers are not ordinarily used for high through-put as is needed for today's large, high speed computers.
Many high speed printers that print on a continuous web of Z-fold computer paper are constructed with a printed computer paper receiving bin directly beneath the paper discharge region of the printer. Because of the Z-fold construction of such continuous web of computer paper, when the paper exits the printer and falls into the bin under gravity, the paper naturally folds back and forth on itself along alternating transverse sheet separation lines so that a stack of sheet-sized printed computer paper is formed, with the top of each page (except the first page) being joined to the bottom of the preceding page. Representative of such high speed printers having integral, printed computer paper stacking bins is the SIEMENS-NIXDORF 2140 Model 3 electronic printing system.
An inherent disadvantage of such printers with integral stacking bins is that the bins necessarily have limited paper stacking capacity. This tends to be less than optimal, particularly when the printers are fed a very long continuous web of computer paper whose length is greater than can be stacked in the stacking bins after printing. As an illustration, my prior U.S. Pat. No. 5,092,573 discloses a Z-fold computer paper feeding apparatus for feeding to a printer a continuous web of computer paper that can have an extremely long length, as is highly desirable for modern high speed printers. Obviously, when the integral bin of a printer having such a bin becomes full (i.e., at most when the paper stack reaches the height of the bin), the stack must be manually removed by a printer operator or attendant. The printer cannot continue to process printed information until this stack removal chore is accomplished. Thus, data center operations are disrupted and the potential through-put of these high speed printers is reduced.
For the above-mentioned reasons, it is desirable to provide a means to accomplish this printed paper removal chore while the printer continues to process printed forms (i.e., continues to print).
Although various patents known to the present inventor disclose apparatus and methods for the stacking of cut sheets of paper or printed articles, commonly called "signatures," they do not disclose apparatus and methods for stacking Z-fold computer paper in an efficient and reliable manner that maintains the integrity of the continuous web of paper. U.S. Pat. No. 4,934,687 to Hayden, et al., for example, discloses a high speed stream fed stacker method and system f or printed products; however, the patent is applicable only to the stacking of printed signatures from a high speed printing press. In such case, all the signatures in a run would be expected to be identical and so there is no necessity for maintaining order, much less continuity between the signatures.
U.S. Pat. No. 3,255,885 to Klingler discloses a signature stacking mechanism for the stacking of printed signatures for packaging, but this patent also is not applicable to the stacking of a continuous web of Z-fold computer paper after it has been printed. In this same line, U.S. Pat. No. 3,160,413 to Faeber discloses method and apparatus for supporting stacks of printed signatures. Again, such apparatus is applicable to individual printed products and in not applicable to the stacking of Z-fold computer paper.
Some high speed printers use a roll feed system whereby the printer discharges the printed paper onto a take-up roll instead of permitting the paper to stack in the usual manner. While such a specialized printing system has the advantage of avoiding paper stacking problems such as those mentioned above, it has the disadvantage that the first printed "sheets" are at the center of the take-up spool and the last-printed sheets are at the outside of the roll formed on such take-up spool. This is in reverse order of what is ordinarily required. Therefore, the printed roll would normally have to be fed either onto a second take-up spool so that the first-printed sheets are the first ones accessible on the second spool or else fed into a special stacking apparatus. While such a specialized printing system has the advantage of avoiding paper stacking problems such as those mentioned above, it has the disadvantage of requiring additional equipment to process the printed roll into individual sheets. This equipment takes up valuable floor space, is not easily moved about, and is expensive to maintain. Moreover, the initial cost of such equipment makes it impractical for most applications.
For these and other reasons, the present inventor had invented a highly efficient Z-fold computer paper handling apparatus that is adaptable for use with conventional high speed printers which normally discharge the printed paper into an integral or associated bin, the inventor's apparatus automatically enabling the stacking of a number of interconnected stacks of paper on a conveyor.